delphi – 根据它们是否存在来声明外部函数

interface

function GetTickCount64: Int64;

implementation

uses Windows,SysUtils;

type
   // Don't forget stdcall for API functions.
  TGetTickCount64 = function: Int64; stdcall;

var
  _GetTickCount64: TGetTickCount64;

// Load the Vista function if available,and call it.
// Raise EOSError if the function isn't available.
function GetTickCount64: Int64;
var
  kernel32: HModule;
begin
  if not Assigned(_GetTickCount64) then begin
    // Kernel32 is always loaded already,so use GetModuleHandle
    // instead of LoadLibrary
    kernel32 := GetModuleHandle('kernel32');
    if kernel32 = 0 then
      RaiseLastOSError;
    @_GetTickCount := GetProcAddress(kernel32,'GetTickCount64');
    if not Assigned(_GetTickCount64) then
      RaiseLastOSError;
  end;
  Result := _GetTickCount64;
end;